Perfusion imaging is an imaging technique which captures the transit of an administered contrast agent through vascular tissue of interest such as a vessel and/or an organ like the heart. Generally, for perfusion imaging, a contrast agent bolus is administered to a patient, and the region of interest of the patient including the vascular tissue of interest is scanned. The contrast agent causes the x-ray density in the vascular tissue of interest to temporarily increase as the contrast agent flows through the vascular tissue. A typical perfusion scan includes acquiring data of the same region, over multiple time intervals, covering contrast agent arrival, uptake and wash out. For cardiac applications, the scan has included acquiring data of the same cardiac phase.
Analysis of the acquired data can be used to determine a perfusion state of the vascular tissue of interest, for example, based on the observations of the contrast agent dynamics in the scan field of view. For cardiac applications, this may include quantifying the contrast agent distribution in the cardiac muscle over time. Such analysis may include determining various perfusion related information for the vascular tissue of interest such as a time-attenuation curve, blood flow, blood volume, mean transit time, maximum upslope, time to peak, etc. This information can be used to identify ischemic tissue and/or differentiate between irreversibly damaged (or necrotic) tissue and potentially reversibly damaged (or at-risk) tissue.
Traditional perfusion imaging included continuously scanning the region of interest from before contrast arrival through contrast washout. More recent perfusion imaging has included temporal intermittent, at equal temporal distances, scanning of the region of interest from contrast arrival through contrast washout. Generally, the frequency of the temporal intermittent sampling is based on the temporal sampling necessary to obtain data suitable for accurately deriving perfusion parameters such as time to peak, maximum upslope, and/or other relevant perfusion parameters. For cardiac applications, this has included scanning during one or more particular cardiac motion phases of interest (e.g., such as a quiet phase) each or every other cardiac cycle.
Unfortunately, computed tomography perfusion imaging exposes the patient to ionizing radiation, which can kill or damage cells and which may increase risk of cancer, and the deposited dose with both continuous and temporal intermittent imaging is considered high, and such imaging generally is not used for screening and/or in routine clinical practice. Furthermore, patients who undergo such imaging typically undergo several follow-up imaging procedures, which increases the cumulative radiation dose. Moreover, simply reducing the temporal intermittent sampling may introduce error in perfusion parameters. Thus, there is an unresolved need for other approaches to further reduce patient dose with perfusion imaging.